The invention relates to an apparatus for detecting lateral irregularities of the rim of a wire spoke wheel, in particular for use in a machine for centering such spoke wheels.
Wire spoke wheels, such as bicycle wheels, generally include a wheel spindle, a hub rotatable on the spindle between two retaining nuts on this spindle, a wheel rim and a plurality of spokes extending between the hub and the rim and secured to the latter by adjustable nipples screwed on the threaded outer ends of the spokes. When building such spoke wheels the spokes threaded in a predetermined manner through holes in the hub and in the rim must be properly tensioned by proper adjustment of the nipples to make the rim circular and concentric with the spindle, that is to correct radial errors, and also to make the rim flat, that is to correct lateral irregularities or so-called flat errors.
Although this truing or centering of wire spoke wheels is still in many cases carried out by hand, machines have been developed for automatically centering spoke wheels. One such machine is disclosed in the Netherlands Patent Application 74.12490 and comprises spindle holding means adapted to receive and fixedly hold the spindle of the wheel to be centered in a fixed radial and axial position while allowing the wheel to be rotated. This machine further comprises means for detecting radial errors of the rim, means for detecting flat errors of the rim, drive means for rotating the wheel step by step past these detecting means, one or more driven nipple turning units for turning the spoke nipples in the one or the other direction, and control means for actuating these nipple turning units in response to a detected radial error and/or flat error of the spoke wheel to be centered. The means for detecting flat errors of the wheel rim comprises two oppositely arranged rim followers or rollers engaging the wheel rim on both sides thereof at one location of its circumference which rim followers are carried by a support which is mounted for free lateral movement in the machine frame whereby on turning the wheel this support is laterally displaced in response to flat errors occurring in the wheel rim, which displacement are a measure of such errors with respect to a radial plane of reference through the center of the wheel hub. The support further carries the nipple turning units together with the drive means therefor. This spoke wheel centering machine has the disadvantage that if at the location of a detected flat error the nipple turning units are moved to engage the spoke nipples adjacent this location to correct the error, it is unavoidable that shocks and mass forces occur having a lateral component which may cause a small lateral deformation and displacement of the wheel rim. This interferes with a correct measurement of the flat error and thus with the correction thereof.